<!DOCTYPE html>
<!-- fieldset with one invalid element and a barred for constraint validation element -->
<html>
  <head>
    <style>
      fieldset:invalid { display: none; }
    </style>
  </head>
 <body>
   <fieldset id="fieldset">
    <input required>
    <input id='i' value='foo' readonly required>
   </fieldset>
 </body>
</html>
